CU Change problems

[dan35]

Hi all this is my first post so sorry if i ramble on a bit!!
My problem is that i have changed an old cu with a dual rcd 17th cu. when the upstairs ring is on one of the rcds and the downstairs ring is on the other and i plug any appliance in it trips the downstairs ring. i have changed the rcd, did IR test on downstairs ring these all worked/appeared fine , but still problem occurs. I have moved all circuits on to one rcd and that seems to solve problem,
any ideas? thanks in advance .dan

 

[m4tty]

Have you definitely put the neutrals on the correct bars or could you have a borrowed neutral

 

[dan35]

neutral bars in cu connected properly. a shared neutral between the two ring mains? going back tomorrow will be testing for that . thanks

 

[Hawk81]

have you done a continuity test on the rings to make sure that the two legs at the board are of the same ring. Seen them muddled up before.

 

[Guest123]

Sounds like a neutral problem for sure. Are you 100% that you had both legs of the same ring connected together on the same RCD, not one leg of one ring and one of the other?

Also, double check the split load kit in the CU, maybe an issue there somewhere.

 

[dan35]

bit more info.... everything works until something is plugged into downstairs ring . its a PME system

 

[nickblake]

dan that sounds like a crossed neutral ,like the others have said a circuit will run fine if you have a crossed or borrowed neutral untill you add a load ,on shared neutrals between ground and 1st floor say when you have 2 rcds and a lighting circuit on each with shared neutrals ,IE neutral to landing light being borrowed from an unstaire light ,if its that this would normally trip both RCD's

 

[dan35]

have checked both legs of both rings and they are in the correct bars . will go back tomorrow with a clear head and check on all the suggestions made thank you all for help..

 

[Hawk81]

definitely sounds like the rings are muddled up. Did you check that when you turn 1 breaker off that ring is off.

 

[dan35]

its an old council property have read on forum before about borrowed neutrals on the 2 way lighting will be checking that for sure!!!!

 

[Spudnik]

Do an IR test between all the neutrals.

That will soon tell ya.